Issue 49

S. Pereira et alii, Frattura ed Integrità Strutturale, 49 (2019) 450-462; DOI: 10.3221/IGF-ESIS.49.43 454 These tests were conducted up to 5% maximum strain for the 0.58mm wire and up to 3% for the 0.25mm wire, using the pin positions given by Tab. 1. Strain 0.58mm wire 0.25mm wire  (mm) Pin 1 (mm) Pin 2 (mm) Pin 3 (mm)  (mm) Pin 1 (mm) Pin 2 (mm) Pin 3 (mm) 0.6% 48.3 -0.66 -0.479 0.516 20.83 -1.53 -1.097 1.155 0.8% 36.25 -0.88 -0.636 0.68 15.63 -2.03 -1.449 1.507 1% 29 -1.1 -0.792 0.84 12.5 -2.53 -1.794 1.846 2% 14.5 -2.19 -1.547 1.589 6.25 -5.02 -3.433 3.403 3% 9.67 -3.26 -2.266 2.271 4.17 -7.47 -4.973 4.843 4% 7.25 -4.33 -2.953 2.906 - - - - 5% 5.8 -5.39 -3.615 3.512 - - - - Table 1 : Pin positions and radius of curvature for the used strain levels. Finite Element Analysis A static structural Finite Element Analysis (FEA) was conducted in ANSYS 19.0 Workbench with the model shown in Fig. 4 to replicate the experiments conducted in the testing machine. The 0.58mm diameter wire was modelled with 10810 elements, and the 0.25mm diameter wire was modelled with 10850 elements, both with superelastic material properties showed in Tab. 1. The wire was clamped at one end and it was deformed under bending using three steel actuator pins that moved in the y direction based on the constant curvature formulation earlier presented. The movement of the actuators was simulated as being gradual, in an explicit iterative way. Contact properties were added between the actuator pins and the wire, with a considered frictional coefficient of 0.2, in order to mimic the experimental procedure [18]. R ESULTS FOR N I T I W IRE Uniaxial Tension and Uniaxial Fatigue Test efore the rotary fatigue tests, the 0.58 specimen was tested under a uniaxial tension test and the results can be seen in Fig. 5, as well as the results, under the same conditions, for two other NiTi alloys [19]. Also, the specimen was subjected to one hysteresis cycle, Fig. 6, and the material properties obtained can be seen in Tab. 2. B Figure 4 : The FEA model with the clamp and the pins.